In earlier years of this project, a background knowledge of genetics of Aedes aegypti was developed, economic traits such as vector competence for malaria and filariasis were analyzed genetically, aspects of hormones and pheromones in reproductive life were demonstrated and promising leads for genetic control were uncovered and tested in the field. In the next five years, emphasis is to be shifted to genetic and ecological studies of the treehole mosquito, Aedes triseriatus, especially in regard to vector competence for La Crosse Encephalitis virus (LAC), the most common form of human encephalitis in the midwest. Mutants will be isolated, chromosomes studied, linkage maps prepared, traits such as ability to transmit LAC analyzed. Preliminary evidence suggests that LAC may hve a deleterious effect on the mosquito, resulting in field selection for virus-resistant forms; EM and FA will be used to check this hypothesis. Field-oriented studies will concentrate on life table budgets and population modeling. Of special importance are egg diapause (factors initiating and breaking), treehole productivity factors and development of better traps for population monitoring. Epidemiology of LAC will be followed at "hot" field sites in Indiana and Illinois. We are looking for an Achilles' heel in the transmission cycle. Among diverse attempts to break transmission, we will make field releases of Toxorhynchites, a giant predatory mosquito that seek out treeholes. A pathogenic gregarine protozoan, Lankesteria, will be released. Manipulation of the sibling species, Aedes hendersoni, a non-transmitter of LAC, may provide another way. Genetic control via disease-refractory genes and/or chromosome translocations will also be studied. Genetic work on Aedes aegypti will continue. In a few years, we expect to initiate studies of vector competence for dengue virus. When dengue-refractory genes have been isolated, field experiments with population replacement by translocations will be started, probably in Puerto Rico in cooperation with CDC. Our W.H.O. Reference Centre, with 35 species and 250 strains of Aedes will continue.